Optoelectronic components on an organic basis, for example organic light-emitting diodes (OLEDs), are being increasingly widely used as a surface light source.
An organic light-emitting diode (OLED) may include on a carrier an anode and a cathode with an organic functional layer system therebetween. In a conventional OLED there are height differences in the range of up to 1 μm on account of the structuring of the anode, the stacking of the layers and resist structures.
The organic constituents of said components are often susceptible vis-à-vis harmful environmental influences, for example water and/or oxygen. For protection against harmful environmental influences OLEDs are surrounded with an encapsulation, for example a thin film encapsulation (TFE). In OLEDs, for example upon the bending of flexible OLEDs, delamination can occur between individual layers within the OLED, e.g. within the TFE, coatings on the TFE, etc., which can lead to a total failure of the OLED. Possible damage mechanisms are for example a delamination of the TFE or the delamination of protective layers, for example of a lacquer, from the OLED carrier.
In the light-emitting area, adhesion is normally provided by the weak adhesion force of the encapsulation layers among one another or towards the two electrode interfaces (e.g. ITO, Al). The adhesion force of the layers is significantly higher in the edge region, since e.g. the encapsulation layers of the TFE are applied directly on the encapsulation layers of the carrier. The adhesion force of the overall component is predominantly determined thereby.
In the automotive sector, (flexible) OLEDs necessitate stringent requirements with regard to reliability and fail-safety, for example thermal cycling tests, harmful gas tests, storage with exposure to moisture under elevated temperature loading, etc. Under extreme test conditions, however, the adhesion force is still insufficient to withstand all the test conditions without faults. Moreover, as a result of the process implementation e.g. during laser processing (laser separation, laser ablation), faults such as delamination of the TFE layers among one another can be induced, which can lead to failure in subsequent tests of robustness.
Furthermore, without measures for coupling out light from the OLED, on account of total internal reflection within the OLED layers, only around 20% of the light generated in the light-generating organic encapsulation layer of the OLED passes to the outside. EP2287938A1 (Lemmer et al.) describes a scattering charge carrier transport layer as a result of the introduction of scattering centres within the active OLED layers. Alternatively, the coupling-out of light is increased by scattering layers having a high refractive index directly adjacent to the transparent electrode.
For OLEDs that emit light through the carrier, an organic semiconductor material is known which crystallizes upon thermal vapour deposition onto underlying organic semiconductor layers. As a result of the morphology that arises in this case, the interface between organic system and metallic electrode vapour-deposited thereon is not smooth, but rather wavy, which prevents the waveguiding in the OLED layers, as known from Pavicic et al., Proceedings Of International Display Week (2011) 459.
Furthermore, a non-planar OLED substrate is known from Koo et al. Nature Photonics 4, 222-226 (2010) (see FIG. 7). FIG. 7 shows a schematic sectional illustration and a micrograph of a conventional organic light-emitting diode (OLED). The schematic cross-sectional view 700 shows a layer stack of an organic light-emitting diode in which the surface of a glass carrier 712 is structured by means of a UV-curable resin 702. An OLED (704-710) is subsequently fabricated on the non-planar substrate surface, i.e. the structuring 702. That is to say that a 120 nm thick ITO layer 704 is formed as an anode on the surface of the structuring 702. A 40 nm thick TPD layer 706 is formed on the ITO layer 704, on which TPD layer a 30 nm thick Alq3 layer 708 is formed as an emitter layer. A 150 nm thick Al layer 710 is formed as a cathode on the Alq3 layer 708. A micrograph 720 of the surface of such a layer stack is shown besides the schematic cross-sectional view 700. It is possible to discern the non-planar surface of such an organic light-emitting diode and, from the image insert, the regularity of the undulation. In the case of the structuring of a surface of a carrier with an organic material there is the risk of a lateral penetration path for oxygen and water through the organic encapsulation layer.